Pneumatic tires with cable bead core

Abstract

A pneumatic tire comprises a bead core formed by laminating three or more sheath layers of spirally twisted sheath filaments around a thick core wire and making reverse the twisting direction of the sheath filament in these sheath layers every the sheath layer, in which the number of twisting pitches in the sheath filament of a second sheath layer viewed from the outermost side is made smaller than that in sheath filament of a sheath layer located inward from the second sheath layer.

What is claimed is:  
     
       1. In a pneumatic tire comprising a bead portion provided with a bead core formed by laminating three or more sheath layers, each of which layers being constituted by substantially spirally twisting a plurality of fine sheath filaments, on a single thick core wire and making reverse twisting directions of the sheath filaments in the sheath layers every the sheath layer, an improvement wherein the number of twisting pitches in a sheath filament of a second sheath layer viewed from an outermost side of the sheath layers is made smaller than that in a sheath filament of a sheath layer located inward from the second sheath layer. 
     
     
       2. A pneumatic tire according to claim  1 , wherein the number of twisting pitches in the sheath filament of the outermost sheath layer is made smaller than that in the sheath filament of the second sheath layer. 
     
     
       3. A pneumatic tire according to claim  1 , wherein the number of twisting pitches in the sheath filament is gradually decreased from the innermost sheath layer toward the outermost sheath layer. 
     
     
       4. A pneumatic tire according to claim  1 , wherein the number of twisting pitches in the sheath filament is decreased stepwise from the innermost sheath layer toward the outermost sheath layer.